This invention relates to a nutation damper system for damping nutation in an artificial satellite.
An artificial satellite comprises a body and at least one antenna mounted on the body and is operable in a mission mode to carry out predetermined flight operations when launched in a space. During the flight operations, the satellite is intentionally or unintentionally rotated or spun like a top around an axis of rotation. It should be noted here that a spin rate and moment of inertia are variable because a mass of the satellite is variable in the mission mode due to consumption of fuel used in the satellite and because a despun motor or the like is operated. As a result, the rotation of the satellite is accompanied by nutation in addition to precession. The nutation is specified by a nutation frequency and a nutation amplitude.
A conventional nutation damper system is carried on the body of the satellite to damp the nutation by the use of an eddy current. More particularly, the conventional nutation damper system comprises a damper unit of a pendulous type comprising, in turn, a conductive plate fixed to the satellite body and a pendulous magnetic piece movable relative to the fixed conductive plate in response to the nutation to induce the eddy current in the fixed conductive plate. The pendulous magnetic piece is swingable at a natural frequency. In order to effectively damp the nutation, the natural frequency should be tuned to the nutation frequency. Otherwise, damping effect of the nutation is unduly reduced. Inasmuch as the nutation frequency is variable in dependency on the spin rate and the moment of inertia, as mentioned above, the damper unit must be constituted so that the nutation frequency determined at a specific one of the flight operations is tuned to the natural frequency of the pendulous magnetic piece. When such a determined nutation frequency is different from a practical nutation frequency, it is impossible to adjust the determined nutation frequency to the practical one. Moreover, another nutation damper unit is indispensable to damp the nutation occurring during another one of the flight operations. Therefore, the nutation damper system inevitably becomes heavy in weight and bulky or intricate in structure.